Schottky Barrier Lowering of Metal/4H-SiC Junction with Ultrathin Aluminum Oxynitride Interlayer*

Silicon Carbide (SiC) has been widely investigated to develop high power electronic devices as a reliable wide band gap semiconductor. The electrical characteristics of SiC Schottky diode depend strongly on the interface energy barrier, and a lower Schottky barrier is advantageous to improve power efficiency and acquire fast switching. We report experimentally that the Schottky barrier of metal/4H-SiC junction is reduced significantly with an ultra-thin (down to ~1.0 nm) aluminum oxynitride (ALON) interlayer inserted at the junction interface. The ultra-thin ALON layer was deposited by using the RF magnetron sputtering with the in-situ flashing to remove the native oxide. High-resolution transmission electron microscope (HR-TEM) images confirmed that the grown ALON film was amorphous. The Schottky barriers of metal/ALON/4H-SiC and metal/4H-SiC junctions were obtained by performing current-voltage (I-V), capacitance-voltage (C-V), and internal photoemission (IPE) measurements. The interface barrier was reduced by up to ~0.8 eV and the reduction was not related to the work-function of metal. The electrostatic potential change driven by the fixed charges in the interlayer or the Fermi-level depinning associated with the suppression of metal-induced gap states is generally known as the origin of Schottky barrier modulation with an interlayer. However, the Fermi-level pinning factor was found to remain almost unchanged in our case, implying that the surface states of 4H-SiC are NOT the main factor of the observed Schottky barrier reduction. The fixed positive charges in the ALON thin film are presumed to cause the reduction.